Method and device for steering a surface compacting machine

Abstract: The invention relates to a steering system for tandem-type surface compacting machines equipped with two independent steering modes, e.g. machines equipped with both frame steering (3) and with individual steering (6) of one of the rollers (4a). The object is to achieve simultaneous control of both systems, one enabled by a steering wheel-activated control valve (11) and the other enabled by a joystick-activated electric control valve (12), arranged, via switching valves (14) which are activatable with an electric switch, in such a way that the machine operator can instantly select the steering system whose activation with the steering wheel or joystick respectively he deems most appropriate at any given moment.

Description: The invention relates to steering systems for tandem-type surface compacting machines equipped with two independent steering modes, i.e. a system in which either the leading or trailing roller can be individually steered, as previously known through US-A-3,868,194 and US-A-4,043,422, or a system permitting frame steering or individual steering of one of the rollers as shown in the German patent DD-A-229 449. Rollers of these types are usually steered via a steering wheel-activated hydraulic control valve which governs the flow of fluid to steering cylinders. Actuating of a switching valve permits selection of the desired steering cylinders, either the cylinders actuating the leading roller or the trailing roller or, in the second instance, the cylinders actuating the frame steering or one of the rollers. According to the patent claims the object of the invention is to achieve simultaneous control of both systems, one by means of a steering wheel-activated control valve and the other by means of a joystick acting on an electrically operated control valve, arranged, via switching valves which can be set with an electric switch, in such a way that the operator can instantly select the steering system whose operation with the steering wheel or joystick he deems most appropriate at any given moment. The steering wheel-activated steering valve has a capacity, appropriate to the roller size in question, by which the steering speed is affected by the speed with which the wheel is turned, and the joystick-activated steering valve is equipped with a throttle providing slower, smoother steering. A frame-steered surface compacting machine is normally steered by having the steering wheel, via its control valve, actuate frame steering, in which the rollers track in tandem because of the frame steering. If a larger effective rolling width is desired, i.e. when the rollers are arranged in echelon, individual steering of one of the rollers can be actuated with the joystick so the roller rotates. When this occurs with the vehicle in motion, the surface compacting machine turns. The steering wheel, which acts on the frame steering, is then rotated to compensate for the turn and maintain a straight course, and the rollers are laterally shifted in one optional direction or the other. The steering valve activated by the joystick can also be used for steering the surface compacting machine during normal operation and then acts on the individually steerable roller. The steering geometry is then affected so the rollers do not track in the same way as in frame steering. This is a major advantage in various tasks, e.g. when the machine closely skirts a curbstone or when a cutting tool is mounted on one of the rollers. The machine operator can instantly select the steering system most appropriate for activation with the steering wheel or joystick at any given moment. The invention will now be described, referring to the attached FIGURES in which FIG. 1 shows a side view of a tandem surface compacting machine. FIG. 2 is a horizontal view of FIG. 1 showing a frame steering joint, an individual steering joint on one of the rollers and steering cylinders. FIG. 3 is a schematic diagram of the hydraulics in one embodiment of the invention. In FIG. 1, the trailing frame section 1 is connected to the leading frame section 2 by the frame steering link 3. The surface compacting machine's trailing roller 4a is carried in the roller frame 5a which is rotatingly carried in the bearing 6 in the trailing frame section 1. The leading roller 4b is carried in the roller frame 5b which is permanently attached to the leading frame section 2. In FIG. 2 is shown the steering cylinders 7 which achieve frame steering via the frame articulation link 3 and the steering cylinder 8, which acts on the roller frame 5a which is individually steerable around the bearing 6, with the roller 4a. FIG. 3 is the schematic diagram of the steering system's hydraulics in which the hydraulic pump 9, equipped with a load-sensing valve 10 via the pressure line CF, is connected to the steering wheel-activated rotary control valve 11 and the joystick-activated electric control valve 12. Before the electric control valve 12 there is an adjustable throttle valve 13 with which an appropriate flow of fluid can be set. The control valve 11 only supplies a flow alternately to the lines R and L when the steering wheel is turned to the right and left respectively. The flow is then proportional to the steering wheel's turning speed. Flow stops when the steering wheel stops turning. Flow through the electric control valve 12 is blocked when the valve is not activated, but when the joystick is moved to the right or left, there is a limited flow through the switching valves 14 to the connected steering system's steering cylinder, causing the surface compacting device to swing to the right or left. As soon as actuation of the joystick ceases, the joystick returns to it neutral position, whereby the electric control valve also returns to its blocked, neutral position. The four switching valves 14 are connected in pairs to the frame steering cylinders 7 and the roller steering cylinder 8 respectively, and their functional positions are changed by an electric switch (not shown) in the cab. By means of pressure-controlled check valves 15, fluid can flow from the non-pressurized part of the steering cylinders 7 back to the control valve 11 when frame steering is activated. If joystick control is activated, fluid flows to the tank 17. In the corresponding manner, the pressure-controlled check valves 16 permit a return flow of oil from the non-pressurized part of the steering cylinders 8. The arrangement of the frame steering system and roller steering system with the two overflow valves 18 and the two check valves 19 is intended to prevent overloading of the steering system if an extremely heavy external load should occur, something which could happen if the rollers struck some solid object such as a curbstone etc.

Claims: A method of steering a tandem surface compacting machine, said machine being equipped with two independent hydraulic steering systems which can be activated by two control systems, whereby said two control systems can be actuated simultaneously by the machine operator to allow simultaneous control of both steering systems, a steering wheel-activated control valve (11) being provided for one control system and a joystick-activated electrically operated control valve (12) being provided for the other control system, said valves (11,12) being arranged in such a way that the machine operator can instantly select, with an electric switch, which of the two steering systems is to be activated by the steering wheel and which of the two steering systems is to be activated by the joystick. A method according to claim 1, wherein the joystick-activated control valve (12) provides the activated steering system with a slow, smooth steering speed, whereas the steering speed of the steering system activated by the steering wheel-activated control valve (11) depends on the speed with which the steering wheel is turned. A device for steering a tandem surface compacting machine, said machine being equipped with two independent hydraulic steering systems which can be activated by two control systems, whereby said two control systems can be actuated simultaneously by the machine operator to allow simultaneous control of both steering systems, a steering wheel-activated control valve (11) being provided for one control system and a joystick-activated electrically operated control valve (12) being provided for the other control system, an electric toggle switch being connected to four switching valves (14) whose sliders simultaneously change position when the toggle switch is tripped, thereby shifting the flow of fluid from the steering wheel-activated control valve (11) from actuation of a frame steering cylinder (7) to actuation of a roller steering cylinder (8), and at the same time shifting the flow of fluid from the joystick-activated control valve (12) from actuation of the roller steering cylinder (8) to actuation of the frame steering cylinder (7). A device according to claim 3, wherein the steering wheel-activated control valve (11) is a rotary valve which, when the steering wheel is turned, affects the flow of fluid to the steering system connected via the switching valves (14) to a degree proportional to the steering wheel's turning speed, and the joystick-activated control valve (12), acting through an adjustable throttle (13) before the control valve (12), generates an even, adjustable flow of fluid to the steering system connected via the switching valves (14).

Inventors: BJOERSNE MATS, SVENSSON BO, BJOERSNE, MATS, SVENSSON, BO, Björsne, Mats
Applicants: SVEDALA COMPACTION EQUIP AB, SVEDALA COMPACTION EQUIPMENT AKTIEBOLAG
Application year: 1994
Main classification: E01C19
IPC codes: B62D12, B62D53, E01C19